Heat exchanger with a mixing chamber

ABSTRACT

A heat exchanger, in particular for a motor vehicle, comprises a collector box and at least one longitudinal row of multi-channel flat tubes through which a first fluid can flow. The collector box is made up of stacked plates including:
         a header plate with at least one row of mounting slots receiving an end portion of each tube,   a distribution plate comprising at least one row of distribution slots,   a cover plate comprising at least one row of collecting apertures which connect at least some of the distribution slots to a manifold, at least one collecting aperture being arranged between two adjacent distribution slots.       

     Said collecting aperture is arranged in a main recess provided in the bottom face of the cover plate.

TECHNICAL FIELD

The present invention relates generally to heat exchanger for motorvehicles.

BACKGROUND OF THE INVENTION

The present invention relates more particularly to a heat exchanger suchas an evaporator, comprising a collector box and at least onelongitudinal row of multi-channel flat tube portions through which afirst fluid such as a refrigerant fluid can flow and around which asecond fluid such as air can flow, said tube portions being flat along atransverse direction and being connected to the bottom face of thecollector box, wherein the collector box is made up of stacked platesincluding:

a distribution plate comprising at least one row of distribution slotswhich distribute the first fluid in the collector box,

a cover plate comprising at least one row of collecting apertures whichconnect at least some of the distribution slots to a manifold, at leastone collecting aperture being a collecting aperture arranged between twoadjacent distribution slots in order to connect jointly said twoadjacent distribution slots to the manifold.

The heat exchanger relates to multi layers collector box assemblies fortwo phases flow products with high pressure withstanding.

Such a heat exchanger is disclosed for example in U.S. 2005/0039901.Nonetheless, the fluid circulation in the collector box is notoptimized. More particularly, the two phases flow is not homogeneouslymixed creating pressure drops and efficiency loss in the heat exchanger.

It is known, for example from FIG. 8, reference 545, in U.S.2005/0039901, to provide the distribution plate with a cutoff portionbetween two adjacent distribution slots in order to connect the twodistribution slots. However, such a cutoff portion tends to weaken thecollector box assembly and to decreases its high pressure withstandingcapability.

SUMMARY OF THE INVENTION

An object of the invention is to provide a heat exchanger with a moreuniform distribution of the first fluid to the tubes and a morepressure-stable construction. The heat exchanger should avoid flowstratification by improving the flow mixing in the collector box.

This object is achieved by a heat exchanger of the above mentioned typecharacterized in that said collecting aperture is arranged in a mainrecess provided in the bottom face of the cover plate in order to formwith the upper face of the distribution plate a mixing chamber for thefirst fluid, said mixing chamber extending at least partially above saidtwo adjacent distribution slots.

Thanks to the main recess forming the mixing chamber, the fluiddistribution is better and there is no need to provide the distributionplate with a large and deep cutoff in order to create a mixing chamber.The advantage of avoiding cutoff in the distribution plate is tomaximize the brazing surface between the distribution plate and theheader plate which provides stronger attachment forces between theplates allowing the use of thinner plates, for example a thinnerdistribution plate.

According to other features of the invention:

-   -   said collector box includes a header plate with at least one row        of mounting slots receiving an end portion of each tube portion,        said distribution plate being arranged between said header plate        and said cover plate,    -   said collecting aperture is of oblong shape along an axis        parallel to the distribution slots,    -   said main recess is of oblong shape along the manifold axis,    -   said manifold is made of one piece with said cover plate,    -   said main recess is stamped in the bottom face of the cover        plate such as to form a bump on the inner surface of the        manifold which creates a section reduction in the manifold,    -   it comprises two rows of tubes and it comprises an inlet        manifold and an outlet manifold,    -   the portion of the distribution plate which faces said        collecting aperture is provided with an additional recess for        enlarging said mixing chamber towards the distribution plate,    -   said additional recess is delimited transversally by two lateral        surfaces which are facing each other, said lateral surfaces        defining an increasing flow section towards each of the two        adjacent distribution slots;

The present invention provides also a method for manufacturing a heatexchanger according to the above mentioned features, comprising thesteps of:

-   -   extruding the cover plate,    -   forming the main recesses in the bottom face of the cover plate        by stamping process,    -   piercing the collecting apertures in the main recesses.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is now described by way of example with referenceto the accompanying drawings in which:

FIG. 1 is an exploded perspective view showing an evaporator accordingto a preferred embodiment of the invention;

FIG. 2 is a perspective view including partial cross-section andlongitudinal-section along 2-2 showing a portion of the evaporator ofFIG. 1;

FIG. 3 is a perspective view including a cross-section along 3-3 showingthe evaporator of FIG. 1;

FIG. 4 is a perspective view showing the cover plate of the evaporatorof FIG. 1 provided with recesses;

FIG. 5 is a view similar to FIG. 1 showing an alternative embodiment ofthe evaporator including U-tubes.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 and 2 show an evaporator 10 for a motor vehicle air-conditioningsystem which is operated with CO₂ as refrigerant according to apreferred embodiment of the present invention. This evaporator 10 isdesigned as a two rows flat-tube evaporator and has a multiplicity offlat tubes 12 arranged along two longitudinal rows R1, R2, a front rowR1 on the front side of the evaporator 10 and a rear row R2 on the rearside of the evaporator 10. These flat tubes 12 can be designed asextruded multi-channel flat tubes, which have a multiplicity of flowpassages 14. All the flat tubes 12 have the same length along a verticalaxis V and the same depth D along a transverse axis T.

In the following description, for the purpose of better understanding,we will use an orientation along the vertical axis V, the longitudinalaxis L, and the transverse axis T, as can be seen on FIG. 1.

Preferably, the flat tubes 12 are multiport extruded flat tubes.

Between the individual flat tubes 12 there are corrugated fins 16, whichare acted on by ambient air in the direction of the arrow F, i.e. alonga transverse axis.

The tubes 12 are fitted between an upper end member constituted of acollector box 18 and a lower end member constituted of a diverter box20.

The collector box 18 comprises a stack of individual plates bearingagainst one another and including successively a cover plate 22 at thetop, an intermediate distribution plate 24, and a header plate 26 at thebottom. The collector box 18 comprises also an inlet manifold 28 and anoutlet manifold 30 which extends along a longitudinal axis, in parallelto each other, and which are made of one piece with the cover plate 22,the cover plate 22 and the manifolds 28, 30 being extruded.

As an alternative embodiment, the cover plate 22 could be stamped andthe manifolds 28, 30 could be made from rolled and welded process, andthen these separates parts would be brazed together.

In the drawings, the header plate 26, in which a front row and a rearrow of mounting slots 32 are arranged, is illustrated above the flattubes 12, the two parallel rows of mounting slots 32 corresponding tothe two rows R1, R2 of flat tubes 12. The mounting slots 32 are locatedone behind the other in the transverse direction and in each case leavebetween them webs 34 which separate two adjacent flat tubes 12 in thetransverse direction. The total number of mounting slots 32 matches withthe total number of flat tubes 12, each flat tube upper end 33 beinginserted into the header plate 26 through a mounting slot 32.

The distribution plate 24, or diverter plate, is arranged above theheader plate 26 and has distribution slots 36 for refrigerant passagesimilar to the mounting slots 32. The distribution plate 24 comprises,in alternation, two distribution slots 36 forming through passages whichlie one behind the other in the transverse direction, leaving a web 40between them, and a diverter passage 42 which continues through in thetransverse direction.

The configuration of distribution slots 36 and diverter passages 42adopts a pattern which repeats itself after four longitudinally adjacenttubes 12, said pattern corresponding to two flow paths 44 through theheat exchanger 10. In each case two adjacent flow paths 44 are arrangedmirror-symmetrically with respect to one another along the longitudinalaxis L. This means that either the distribution slots 36 of a flow path44 come to lie next to the distribution slots 36 of an adjacent flowpath 44, or a diverter passage 42 of a flow path 44 comes to lie next toa diverter passage 42 of an adjacent flow path 44. The diverter passages42 have a cross-over function, allowing the refrigerant to transfer fromone row R1 to the next R2 within air stream direction F.

A flow path 44 of the refrigerant follows the direction of the arrowsalong the dashed-line 44, i.e. the refrigerant enters the front tube 12at A passing into the distribution slot 36, initially flows downward, isdiverted at the bottom B, then flows upward through a longitudinallyadjacent front tube 12 and passes into the diverter passage 42 at C,where it is diverted, before then flowing downward on the rear side ofthe evaporator 10, where it is diverted at D and then flows upward againin order to pass through the distribution slot 36 of the adjacent reartube 12 as indicated by arrow E. The supply and discharge of therefrigerant is described on the basis of FIG. 2.

According to the present embodiment, each flow path 44 is diverted atthe bottom part of the evaporator 10 thanks to the diverter box 20 whichis aimed to redirect (at B and D) the flow coming downward through aflat tube 12 towards the longitudinally adjacent flat tube 12 in theupward direction as if the evaporator was formed from individualU-tubes. An example of a similar diverter box 20 is disclosed in U.S.2005/0039901 in connection with FIG. 1 where it is used for divertingthe flow from the front row of tubes towards the rear row of tubes(paragraphs [74] and [75]).

According to an alternative embodiment, the diverter box 20 could beomitted by providing the heat exchanger 10 with U-tubes 21, as shown onFIG. 5, instead of straight flat tubes 12. The U-tube 21 comprises twovertical portions linked at the bottom by a bended portion extendinglongitudinally.

What is referred to as a cover plate 22, which includes two parallelrows of collecting apertures 46, 48 is illustrated in the drawing abovethe distribution plate 24. The collecting apertures 46, 48 comprise afirst row of refrigerant inlet apertures 46 connecting the distributionslots 36 underneath to the inlet manifold 28 and a second row ofrefrigerant outlet apertures 48 connecting the distribution slots 36underneath to the outlet manifold 30.

According to the present embodiment, each collecting aperture 46, 48 isarranged above and between two longitudinally adjacent distributionslots 36 in order to connect jointly said two adjacent distributionslots 36 to the corresponding manifold 28, 30.

The above-described individual parts of the evaporator 10 are assembledin the following way. The header plate 26 is fitted onto the flat-tubeends 33. Then, the distribution plate 24 and the cover plate 22 with themanifolds 28, 30 are stacked on top of the header plate 8.

The different plates constituting the diverter box 20 at the bottom ofthe evaporator are assembled in a similar way.

As an alternative embodiment, the distribution plate 24 could beintegrated into the header plate 26 to save one plate.

After the evaporator 10 has therefore been assembled, it is soldered toform a fixed block in a soldering furnace. During the soldering process,the plates 22, 24, 26 are held in position with respect to one anotherby a positive or non positive clamping action. However, it is alsopossible firstly to assemble the end member comprising header plate 26,distribution plate 24, and cover plate 22, and then to connect it toflat tubes 12.

According to the invention, each collecting aperture 46, 48 is arrangedin a main recess 50 provided in the bottom face 52 of the cover plate 22in order to form, with the upper face 54 of the distribution plate 24, amixing chamber 56 for the refrigerant. As can be seen on FIG. 2, saidmixing chamber 56 extends partially above the two adjacent distributionslots 36 and said main recess 50 is made longitudinally larger than thecollecting aperture 46, 48.

Preferably, the recess 50 is made by stamping process into the bottomface 52 of the cover plate 22 which provides the corresponding manifold28, 30 with a bump 58 on its inner surface 60. The bump 58 is delimitedtransversally by the inner transversal dimension of the manifold 28, 30.More particularly, the bump 58 is delimited transversally by thelongitudinal tubular wall 62 of the manifold 28, 30, at the location 63where the tubular wall 62 is linked to the cover plate 22. The verticaldepth of the main recess 50 may be approximately the thickness of themetal plate constituting the cover plate 22.

Advantageously, the main recess 50 has a dome shape which allows anoptimized distribution.

According to the embodiment shown, the main recess 50 is of longitudinaloblong shape so that it extends longitudinally from the middle of onedistribution slot 36 to the middle of the adjacent distribution slot 36.

The collecting apertures 46, 48 are preferably designed as bores oftransversal oblong shape with dimensions matched to the desiredrefrigerant distribution and quantitative flow. The oblong shape extendstransversally which allows a better distribution/collection of therefrigerant into all the channels 14.

The section of the collecting apertures 46, 48 is preferably rangedbetween 30% and 60% of the total open area of the tubes 12 to feed. Thisrestriction is done by purpose to make sure the refrigerant flow is moreor less constant up to the far end of the manifolds 28, 30. The sectionrestriction is adjusted longitudinally, from one collecting aperture 46,48 to the others, depending on the manifold 28, 30 length and/ordepending on refrigerant flow length in the tubes 12.

In addition to the preferred range 30% -60%, the evaporator 10 isdesigned for obtaining good performances at some predefined operatingpoints which help to define the final value for the section of thosecollecting apertures 46, 48.

Thanks to the mixing chambers 56 connected to the inlet manifold 28, therefrigerant is able to mix before flowing into the two connected tubes12 which makes the refrigerant more homogenous, in terms of pressure andin terms of fluid consistency, all along the evaporator 10 and all alongeach flow path 44, thus avoiding risks of flow stratification. Flowhomogeneity contributes for an optimized distribution in the evaporator10.

After entering into the collecting aperture 46 and before entering intothe corresponding flat tubes 12, the refrigerant flow impacts on theportion of the distribution plate 24 which faces the collecting aperture46, thus contributing to mixing.

According to a preferred embodiment, the portion of the distributionplate 24 which faces the collecting aperture 46, 48 is provided with anadditional recess 64 for enlarging vertically the mixing chamber 56. Theadditional recess 64 is delimited longitudinally by two adjacentdistribution slots 36 and transversally by two lateral surfaces 66, 68which are facing each other. The greater transversal dimension of saidadditional recess 64 is inferior to the transversal depth of thecorresponding through-passages 38.

Said lateral surfaces 66, 68 define an increasing flow section towardseach of the two adjacent distribution slots 36, the distance betweensaid lateral surfaces 66, 68 increasing towards each of the distributionslots 36. As can be seen on FIG. 2, each lateral surface 66, 68 has atriangular profile from an elevation view. The vertical thickness of theadditional recess 64 is inferior to the thickness of the main recess 50.

Thanks to the additional recess 64, the mixing chamber 56 is enlargedbackwards and allows better distribution in the tubes 12 of the frontrow R1, and better collection from the tubes 12 of the rear row R2.However, the invention could be implemented without additional recesses64.

The use of an additional recess 64 and a main recess 50 instead ofproviding the distribution plate 24 with a cut-off or aperture betweenthe two adjacent distribution slots 36 allows a more strong attachmentbetween the distribution plate 24 and the header plate 26 since thecontact surface 70 for brazing is maximized.

The flow restriction provided in the manifolds 28, 30 by the bumps 58promotes flow turbulences in the manifold 28, 30 which ensure that therefrigerant remain biphasic with an improved flow homogeneity versusstratified one. The bumps 58 provide some kind of diaphragm whichimproves the flow mixing in the manifolds 28, 30.

The use of a bump 58 of oblong shape along the axis of the manifolds 28,30 allows not deforming the longitudinal wall of the manifolds 28, 30.

The main recesses 50, the bumps 58, and the additional recesses 64 havebeen described mainly in connection with the inlet manifold 28 and theinlet apertures 46, i.e. in connection with the inlet side or front sideof the evaporator 10. Symmetrically, the main recesses 50, the bumps 58,and the additional recesses 64 can be provided, all together orselectively, on the outlet side or rear side of the evaporator 10, inconnection with the outlet manifold 28 and the outlet apertures 48.

The present invention has been described in part on the basis of theexample of an evaporator 10. However, it should be noted that the heatexchanger according to the invention is also suitable for other uses.

1. Heat exchanger, in particular for a motor vehicle, comprising acollector box and at least one longitudinal row of multi-channel flattube portions through which a first fluid such as a refrigerant fluidcan flow and around which a second fluid such as air can flow, said tubeportions being flat along a transverse direction and being connected tothe bottom face of the collector box, wherein the collector box is madeup of stacked plates including: a distribution plate comprising at leastone row of distribution slots which distribute the first fluid in thecollector box, a cover plate comprising at least one row of collectingapertures which connect at least some of the distribution slots to amanifold, at least one collecting aperture being arranged between twoadjacent distribution slots in order to connect jointly said twoadjacent distribution slots to the manifold, characterized in that saidcollecting aperture is arranged in a main recess provided in the bottomface of the cover plate in order to form with the upper face of thedistribution plate a mixing chamber for the first fluid, said mixingchamber extending at least partially above said two adjacentdistribution slots.
 2. Heat exchanger according to claim 1,characterized in that said collector box includes a header plate with atleast one row of mounting slots receiving an end portion of each tubeportion, said distribution plate being arranged between said headerplate and said cover plate.
 3. Heat exchanger according to claim 1 or 2,characterized in that said collecting aperture is of oblong shape alongan axis parallel to the distribution slots.
 4. Heat exchanger (10)according to any of the preceding claims, characterized in that saidmain recess (50) is of oblong shape along the manifold axis.
 5. Heatexchanger according to anyone of the preceding claims, characterized inthat said manifold is made of one piece with said cover plate.
 6. Heatexchanger according to claim 5, characterized in that said main recess(50) is stamped in the bottom face of the cover plate such as to form abump on the inner surface of the manifold which generates a sectionreduction in the manifold.
 7. Heat exchanger according to anyone of thepreceding claims, characterized in that it comprises two rows of tubesand in that it comprises an inlet manifold and an outlet manifold. 8.Heat exchanger according to anyone of the preceding claims,characterized in that the portion of the distribution plate which facessaid collecting aperture is provided with an additional recess forenlarging said mixing chamber towards the distribution plate.
 9. Heatexchanger according to claim 8, characterized in that said additionalrecess is delimited transversally by two lateral surfaces which arefacing each other, said lateral surfaces defining an increasing flowsection towards each of the two adjacent distribution slots.
 10. Methodfor manufacturing a heat exchanger according to anyone of claims 1 to 9,comprising the steps of: extruding the cover plate, forming the mainrecesses in the bottom face of the cover plate by stamping process,piercing the collecting apertures in the main recesses.